In the manufacture of biscuits by the cutting method, wherein dough is formed into a continuous sheet which is gauged to the desired thickness by passage through a pair of gauge rollers having a pre-set gap and then fed to cutting apparatus which cuts the biscuit shapes from the continuous sheet, it is very important to present the cutting section of the biscuit forming plant with a dough sheet of constant thickness so that biscuits cut from the sheet will be of a constant weight. Constant weight of cooked biscuits is the aim of all biscuit manufacturers as it enables them to produce packs of wrapped biscuits as close as possible to the minimum weight required by present legalisation.
It is known that the thickness of a sheet of dough emerging from between a pair of gauge rollers, set with the gap between them at a constant desired size, is dependent upon the quantity of dough being fed to the rollers. It is possible to over-feed and under-feed and yet produce a sheet across the full width of the gauge rollers on the output side thereof, but as sheet thickness is dependent upon the correct rate of feed, the sheet would be unacceptable.
In ideal operating conditions the sheet passing through the gauge rollers spreads out as far as flanges provided on both edges of one of the rolls and any slight over-feed will flow backwards. With a significant over-feed the compression of the dough, as it passes between the rollers, increases since the dough, due to its elasticity, tends to revert, on the output side of the rollers to a thickness greater than that desired. This is termed spring or recovery of dough. Also with over-feed the amount of work put into the dough by the increased compression tends to change its characteristics and this can be detrimental to the quality of the cooked biscuits.
Under-feed can result in the gauge rollers tending to pull the sheet and stretch it so that undesirable tension is set up in the sheet before it passes between the rollers. Under-feed can result in the sheet spreading out to the flanges but being thinner at the edges than in the centre, so that some of the biscuits cut from the sheet will be too thin to be acceptable. As the under-feed increases, the sheet can in extreme circumstances become narrower than the required width and not spread completely across the width of the gauging rollers.
It is known to sense these variations in the dough feed conditions by measuring the thickness of the sheet before and/or after the gauge rollers and using the resulting information to effect control of the feed. The measuring devices can be of the contacting type such as wheels or skids running on the dough surface, or may be non-contacting optical sensors, such as those disclosed in British Pat. No. 1484996. The signals derived from these measuring devices can be used, for instance, to control a variable speed motor driving a belt conveyor feeding the dough sheet to the gauge rollers.